StoneTrades — March 30, 2026

The Natural Stone Institute (NSI) has formally revised its ANSI/NSI 373 Sustainable Production standard, with the updated criteria taking effect across all certified operations beginning Q1 2026. The revisions raise baseline requirements for Environmental Product Declarations (EPDs), quarry chain-of-custody audits, and material transparency reporting — changes that directly affect how architects and specifiers qualify natural stone for LEED v4.1 and the forthcoming LEED v5 rating systems.

What Changed in the ANSI/NSI 373 Update

ANSI/NSI 373, first published in 2012 and last substantively revised in 2020, has long been the primary voluntary sustainability certification pathway for natural stone producers. The 2026 update introduces three material changes.

First, third-party verified EPDs are now mandatory for certification at all tier levels — not just the highest tier. Previously, only Tier 3 (exemplary performance) required a full ISO 14025-compliant EPD with a product category rule (PCR) specific to natural stone. From 2026, Tier 1 and Tier 2 operations must also publish EPDs, with a compliance window extending to mid-2027 for existing certificate holders.

Second, quarry chain-of-custody documentation requirements have been strengthened. Processors must now be able to trace finished slabs back to a named quarry and quarry block number, with audit evidence updated annually. This is a direct response to growing demand from project owners and ESG-focused procurement teams who need documented material provenance — not just a generic natural origin declaration.

Third, the updated standard introduces social responsibility indicators aligned with the broader NSI Accreditation framework, including minimum worker safety thresholds and community impact disclosure. These are scored but not yet mandatory for certification; NSI has indicated they will become required criteria in the 2028 revision cycle.

How the Changes Affect LEED Credit Qualification

Natural stone has historically performed well on LEED Material and Resources credits, particularly MR Credit: Building Product Disclosure and Optimization (BPDO). That pathway credits products with publicly available EPDs and those with optimized environmental performance relative to industry average benchmarks.

Under LEED v4.1, a product with a third-party verified, product-specific EPD that meets ISO 14025 requirements and references an applicable PCR counts as one full product contribution toward the 20-product threshold for the BPDO Optimization credit. The NSI 373 update effectively means a broader pool of certified stone suppliers can now make that contribution, since EPD publication is no longer confined to top-tier operations.

The anticipated LEED v5 framework, currently in its public comment phase, is expected to require supply chain transparency as a prerequisite for certain material credits — not just as optional documentation. If finalized in its current draft form, the NSI 373 chain-of-custody requirement (linking finished product back to a named quarry) would align directly with that prerequisite language. Specifiers working on projects targeting LEED v5 certification should be tracking both developments in parallel.

One practical complication: EPDs for natural stone reflect the production and processing profile of a specific quarry and processing facility. A Spanish Crema Marfil slab processed in Alicante and a Crema Marfil slab from the same quarry but cross-cut in a third country will carry different EPD profiles. Architects specifying stone by aesthetics and relying on a single generic EPD to cover multiple sourcing options will face documentation gaps under the updated NSI criteria.

What This Means for Stone Buyers and Specifiers

For procurement teams and project specifiers, the practical takeaway is straightforward: stone that is not NSI 373 certified — or cannot demonstrate equivalent EPD documentation — will face increasing friction on LEED projects as credit requirements tighten.

This affects a wide range of natural stone categories. Marble varieties sourced from Italian and Turkish quarries are the most likely to already have NSI-certified supply chains; the Turkish travertine sector has seen steady growth in certified operators since 2021. Chinese granite — including widely specified varieties such as China Green and imported Indian origins — has had historically lower EPD adoption, though this is changing as more processors pursue NSI accreditation to serve export markets.

From a procurement standpoint, the updated standard changes the questions buyers need to ask at the RFQ stage:

  • Is the supplier NSI 373 certified, and at which tier?
  • Is a current, publicly posted EPD available for the specific material and processing facility?
  • Can the supplier provide quarry block traceability documentation — not just a country-of-origin certificate?
  • Is the EPD product-specific or a generic industry-average declaration?

The manufacturing process matters here too. Gang-saw cut slabs and CNC infrared-cut components processed at different facilities may carry different embodied carbon profiles within the same quarry material. Buyers who dry-lay stone and inspect for batch consistency before shipment — standard practice for large-format marble and travertine orders — should also request EPD documentation at the block-sourcing stage, not after fabrication. Seaworthy packaging and export logistics carry embedded carbon as well; while NSI 373 does not yet require EPD scope to extend downstream to crating and freight, LEED v5 draft language suggests life-cycle scope may expand in future credit iterations.

Industry Response and Implementation Timeline

The NSI Technical Committee published the revised ANSI/NSI 373 language in late 2025 following a comment period that drew responses from producer associations in Italy, Turkey, India, and the United States. The phased compliance timeline — with existing Tier 1 and Tier 2 certificate holders given until June 2027 to publish conforming EPDs — was a direct concession to smaller quarry and processing operations that lack the internal resources to commission third-party life-cycle assessments quickly.

Several major stone trade associations have announced guidance programs to help members through the EPD commissioning process. The Italian marble sector, represented in part through Confindustria Marmomacchine, had already been pushing EPD adoption ahead of EU construction product transparency requirements. The NSI update reinforces that direction from the North American market side.

For buyers with active LEED project pipelines, the window between now and mid-2027 is the practical opportunity to audit existing supplier relationships and identify certification gaps. Operations that cannot demonstrate NSI 373 compliance or an equivalent EPD pathway by that point may find themselves excluded from specification lists on public and institutional projects where LEED credits carry contractual weight.

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